Compound semiconductor epitaxial substrates are used for the producing devices such as high electron mobility field-effect transistors (HEMTs), pseudomorphic HEMTs (pHEMTs), strain quantum well laser devices, hetero bipolar transistors (HBTs) which are used as switches in cellular phones and so on. Such compound semiconductor epitaxial substrates are produced by epitaxially growing on single crystal substrates compound semiconductors with lattice constants different from those of the single crystal substrates.
In a case where compound semiconductors with lattice constants largely different from those of single crystal substrates are grown on the single crystal substrates, the layers of the semiconductors do not grow or even if the layers grow, a large amount of dislocation occurs due to the occurrence of lattice relaxation. Because of this, compound semiconductor epitaxial substrates made by using such compound semiconductors have not been heretofore used for producing those devices.
On the other hand, in a case where substances with lattice constants slightly different from those of single crystal substrates are grown on the single crystal substrates, when the substances is sufficiently thin, the occurrence of dislocation is prevented due to the strain of their lattices, and therefore the substances can be epitaxially grown on the single crystal substrates. However, in the compound semiconductor epitaxial substrates thus obtained, warpage occurs due to stress resulting from lattice strain which occurs in the crystal lattices the compound semiconductors.